Method for Reducing NOx Emissions from Ethanol-Blended Diesel Fuels

ABSTRACT

A method to reduce NO x , emissions from diesel fuel alcohol microemulsions (E-diesel) is taught. Ethanol is stripped from the microemulsion and entered into the exhaust gasses upstream of the reducing catalyst. The method allows diesel engines to meet new, lower emission standards without having to carry separate fuel and reductant tanks.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 10/361,432filed Feb. 10, 2003.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

This invention was made with United States Government support underContract No. DE-AC05-00OR 22725 between the United States Department ofEnergy and UT-Battelle, LLC, and the United States Government hascertain rights in this invention.

FIELD OF THE INVENTION

This invention relates to control of pollution from diesel engines andparticularly to methods for enhancing the catalytic reduction of oxidesof nitrogen by extracting ethanol from E-diesel for injection into theengine exhaust.

BACKGROUND AND PRIOR ART

Diesel-cycle engines have displaced Otto-cycle internal combustionengines in medium and heavy truck use and are becoming increasinglypopular for passenger vehicles. The diesel is inherently more efficientbut its lack of responsiveness, its noise and its distinctive odorhistorically limited its appeal to commercial trucks and businesstraveling salesmen and taxicab fleets. The advent of laws andregulations addressing emissions from “mobile sources” also limited theappeal of diesel cars and light tracks because they were perceived asdirty and regional regulations relating to emissions, especially soot,limited their availability. The Otto-cycle engines were easier to modifyto comply with more stringent emissions requirements in part becausethere are more adjustable parameters and soot is not an issue. Recentadvances in fuel injection management in combination with electronicsystems have closed the gap but the strategies applied to Otto-cycleengines do not always work with diesels.

Oxygenates such as MTBE and ethanol are frequently blended into gasolineto meet air pollution regulations. Ethanol is preferred because it is arenewable resource, is less toxic and politically popular since it ishome-grown and its use is a subsidy for farmers. Ethanol is readilyblended into gasoline, but is difficultly blended into diesel fuel whichhas a blend of thousands of paraffinic, naphthalenic and aromatichydrocarbons ranging in carbon numbers between 10 and 22.

Control of emissions from heavy duty diesel trucks and urban buses hasbecome more stringent in recent years and will become more stringent in2004, when emissions of oxides of nitrogen (NO_(x)) must be reduced to2.0 g/bhp-hr and in 2007 when NO_(x) will be reduced to 0.2 g/bhp-hr. Toachieve the latter levels and to allow for improved particulate matter(soot) traps and NO_(x) catalysts, ultra low sulphur fuel (15 ppm) willbe phased-in in 2006. Alternative fuel blends and efficient catalystswill be required.

WO 93/24593 discloses a stabilized, auto-igniting alcohol-containingfuel for use as a diesel fuel having 20 to 70% by volume lower orderalcohol (ethanol), 30 to 80% by volume diesel fuel, 4.5 to 5.5% byvolume higher order alcohol surfactant, 1 to 15% of a tertiary alkylperoxide, 3% alkyl peroxide and 0.05 to 0.1% by volume of ananti-clogging additive.

U.S. Pat. No. 6,068,670 discloses an emulsified fuel including waterwhich is more stable than that disclosed in French patent applicationserial number 2 470 153 which included water and ethanol and was deemedto be unstable on storage.

U.S. Pat. Nos. 6,190,427 and 6,306,184 disclose an E-diesel fuel whichis believed to be a product commercially available at this time. Thefuel contains 3 to 18% ethanol, 6.5 to 10% of a stabilizer (ethoxylatedfatty alcohols), and the remainder commercial No. 2 diesel oil.Optionally, an alkyl ester of a fatty acid and a cosolvent may be added.

U.S. published patent application 20020104256 is directed to theaddition of oxygenates to ultra low sulphur automotive diesel oil(ULSADO), the form which will be required by 2006. Accepting thepresumption that oxygenates reduce the production of particulates(soot), the reference discloses the use of oxygenates which aresaturated, monohydric alcohols having 4 to 20 carbon atoms.

WO 02/059236 discloses compositions to stabilize hydrocarbon fuel over arange of alcohol and water concentrations as an emulsion and includesthree different non-ionic surfactants. Optionally, a cetane improver maybe employed.

A persistent problem for diesel engines has been production of oxides ofnitrogen, typically a mixture of NO and NO₂ most frequently referred toas NO_(x). While oxides of sulphur can be reduced by using ULSADO, theprimary source of NO_(x) is nitrogen in the air and the highertemperatures of lean burn engines exacerbates an already known problem.Catalysts will be required.

Methods are known to reduce NO_(x) to N₂ and H₂O. The most establishedmethods use ammonia, isocyanic acid or precursors such as urea.Representative examples are U.S. Pat. Nos. 6,203,770; 6,066,303; and4,403,473 and published patent application 20020152745.

Ammonia is a viable and affordable method for controlling NO_(x) atfixed sources but is impractical for mobile sources, especiallymid-sized and compact cars. The proven methods require introduction ofthe reductant downstream of the reducing catalyst, require separatestorage of fuel and reductant, thereby requiring inter alia, separatefueling streams.

An alternative reducing system uses hydrocarbons as the reductant. Thehydrocarbon may be separate from the diesel fuel as disclosed in U.S.Pat. No. 6,006,515 and in SAE Paper No. 2000-01-2823, or a slip streamfrom the fuel. The disadvantage of such a system is that fuel economy isimpacted and the fuel must be carefully metered to avoid hydrocarbonemissions.

A second alternative is the use of ethanol as a reductant. According toPat. Nos. 6,030,590; 6,045,765; 6,057,257; 6,129,713 and 6,284,211 aswell as SAE paper 2001-01-1935. The ethanol is introduced between theexhaust valve and the catalyst, which is taught to be a silver compound.The Caterpillar DeNO_(x), catalyst system, available since 1996, usessuch a protocol. The use of ethanol, a liquid, is less difficult thanammonia systems, less sensitive to control metering than hydrocarbons,but still requires a separate tank and a duel fueling capacity atfueling stations.

There remains a need to develop an efficient system for NO_(x), controlin a single ULSADO fuel.

BRIEF DESCRIPTION OF THE INVENTION

It is an object of this invention to provide a means for reducingNO_(x), in a diesel exhaust. It is a further object of this invention touse a single fuel for both the power source and for the control ofNO_(x) using selective catalytic reduction (SCR). It is a furtherobjective of this invention to separate components of a commerciallyavailable diesel fuel to maximize fuel economy and emissions control.

These and other objectives are obtained by providing a method forstripping a portion of the ethanol in E-diesel and injecting theextracted ethanol into the exhaust stream downstream of the exhaustvalve but upstream of the SCR. Advantageously, the stripping of ethanolmay be accomplished using heat from the diesel engine and manifoldvacuum to lower the distillation temperature of the ethanol(non-turbocharged engines)

Additionally, the method steps to reduce NO_(x) emissions from theexhaust of E-diesel engines with a selective catalytic reducingconverter are; distilling out a portion of the ethanol in the E-dieselunder reduced pressure, injecting the distilled ethanol into exhaustgasses from the engine upstream of the selective catalytic reducingconverter, and controlling the ethanol injection using at least oneengine parameter selected from the group consisting of intake air flow,fuel mixture richness, engine operating temperature and NO_(x) sensoroutput.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of the basic components of the invention.

FIG. 2 is a more detailed diagram showing the components.

DETAILED DESCRIPTION OF THE INVENTION

Commercial E-diesel such as that available fro Pure Energy Corporationcontains approximately 15% ethanol, 1.5% a “proprietary additive”designed to stabilized the fuel and 80-84% low sulphur No. 2 diesel.ASTM standard D975 specifies minimum standards for “diesel fuel,”including boiling point ranges. Accordingly to the standard for lowsulphur No. 2, 90% of the fuel must distill between 282 and 338° C.Typically, the majority boils between 250 and 300° C. Ethanol boils at78.5° C. at 760 mmHg. It has been found by experiment that 90% of theincluded ethanol can be stripped at a temperature of 80° C. This finalproduct contains 95% by volume ethanol and 5% by volume hydrocarboncomponents. Since both ethanol and light hydrocarbons are effectivereductants using available SCR catalysts, the stripped mixture need notbe chemically pure to reduce NO_(x).

Suitable selective catalyst reducing (SCR) materials suitable for usewith ethanol include alumina-supported tin or tin oxides as disclosed inU.S. Pat. No. 6,030,590 and silver based catalysts as described in U.S.Pat. Nos. 6,045,765; 6,057,259; and 6, 284,211 and in SAE papers2000-01-2813 and 2001-01-1935, all incorporated herein by reference.However, because catalyst materials need to be developed in associationwith the reductant type, different fuel-borne reductants (i.e. propane,butane, etc.) would likely require other catalyst formulations foroptimal NO_(x) conversion.

The chemical process whereby NO and NO₂ are reduced on catalysts havebeen studied but a series of actual steps has been postulated only.Multiple steps are known to be involved and they have been shown to varyby type of catalyst, type of support, chemical nature of the reductantand temperature of the catalyst. An excellent review is R. Burch et al.,Applied Catalysis B: Environmental 39, 283 (2002). Each control systemof SCR and reductant must be optimized to maximize N₂ yield whileminimizing N₂0 (a potential greenhouse gas) and NH₃. Optimizationincludes matching the amount of reductant to the concentration of NO, inthe exhaust at a given time and maintaining the temperature of the SCRcatalyst to maximize conversion to N₂. The inherent difficulty inreducing the NO, lies in the fact that modern compression ignitioninternal combustion engines operate using the lean-burn principle tomaximize fuel economy and the exhaust gas contains an excess of oxygen(5-8%) so that the reduction must take place in a nominally oxidative(not reducing) atmosphere. Hence, multiple processes occur on or nearthe catalyst and oxides are inevitably included in the process whichmust be carefully controlled to limit or eliminate conversion to gaseousNO, NO₂, or N₂0.

FIG. 1 is a schematic showing the basic components of the system.E-diesel fuel in tank 3 is normally delivered by fuel line 5 to engine7. Exhaust 9 is directed by a header to an SCR catalyst bed 11 anddischarged through tailpipe 13.

A distillation chamber 15 is connected to tank 3 by line 17. Thedistillation chamber is connected to a stripped ethanol receiver 19 fromwhich it is metered through line 21 to injector 23 in the exhaustheader. The residue from distillation is returned to fuel tank 3 throughreturn line 25.

The still 15 may be a single metallic chamber heated by engine coolantor by a mantle containing a resistance wire heater or by a tubularresistance heater immersed in the fuel. A short packed column and acondenser would connect to receiver 19. In this mode the batchdistillation could be repeated periodically based on engine hours or thelevel of stripped ethanol in the receiver.

Advantage may be taken of the design for fuel systems in modern dieselengines. FIG. 2 illustrates the components in greater detail. Fuel fromtank 103 is pumped through a filter/heater 104 which warms the fuelusing re-circulated engine coolant and removes particulates is deliveredthrough fuel line 105 to pressurized fuel rail 106 from which it isinjected into the engine 107. The exhaust 109 may or may not passthrough a turbocharger (not shown) to SCR catalyst bed 111 beforepassing through tailpipe 113. Fuel exiting the rail 106 is split into areturn line 118 and a sample line 117. The return line 118 circulatesfuel through line 125 back to tank 103. The sample line 117 carries fuelto distillation chamber 115. A heater 131 which may be electric or usecirculated coolant (or both) fractionates the fuel into a primarilyethanol fraction and a diesel fraction. The ethanol-rich fraction iscondensed using condenser 133 and directed to receiver 119. The residueis returned to the tank 103 through return line 125.

When manifold vacuum is not regularly available, an electric vacuum pump135 may be used to reduce the heat requirement for distillation.

A float or other sensor in receiver 119 may be used to start and stopthe stripping process such as by turning off heat to heater 131,adjusting the split between lines 117 and 118 or by returning strippedethanol to the main tank 103. A small electric pump 137 pressurizeslines 138 to ethanol injection 123. A recirculating line 139 maycirculate ethanol back to receiver 119.

The stripped ethanol may be injected into the exhaust near the exhaustport or downstream, near the SCR catalyst bed. For motors with exhaustgas recirculation, the downstream location is preferred, for greatercontrol of the NO_(x): EtOH ratio. In the preferred embodiment, meanssuch as a water jacket may be used to protect the injector from heatdamage.

There are currently 17 different test cycles in use to test emissionsfrom diesel-powered vehicles. All involve engine or chassis dynamometersand are designed to duplicate operational cycles such as the OrangeCounty Bus Cycle for transit buses. Europe currently has five testcycles; Japan four. ISO 8178 is used for some off-road certifications.The AVL 8-mode heavy-duty cycle is a steady-state engine test proceduredesigned to correlate closely with the emission results obtained usingthe U.S. FTP transient cycles for heavy duty trucks using an enginedynamometer. The AVL 8 is a weighted average of eight differentcombinations of engine speed and load and provides results moreconveniently than the FTP transient protocol.

The amount of ethanol required to sufficiently reduce NO_(x) emissionsover a catalyst depends on the NO_(x) flux which, in turn, is dependenton the engine operating regime. Engine experiments showed that 3 partsethanol is required to reduce 1 part NO_(x) (mole: mole basis). UsingAVL 8-mode as a guideline, then approximately 38.6 ml of ethanol isrequired for 1000 ml of fuel. This means that approximately 3.86% of theethanol in a 15% E-diesel fuel is required for proper mass balance. Thisresults in 11.4% of the original ethanol being unused by the SCR systemand therefore consumed by the engine from a 15% blend.

In actual use, it is envisioned that a dynamic ethanol injection systemwould be employed based upon various engine parameters such as intakeair flow, fuel mixture richness, operating temperature and probably anNO_(x) sensor in the exhaust.

The data would be processed utilizing available computer processors andadjustable parameters changed accordingly to optimize efficiency. Sinceit is necessary to control the temperature of the catalyst under variousload conditions but especially at idle and start-up, the reductant maybe used to provide heat through combustion in the exhaust under leanconditions. An ignition source such as a spark plug or glow plug may beused for this purpose to initiate burning of some of the reductant toprovide such heat. Optionally, an oxidizing catalyst may be used betweeninjector and SCR catalyst to increase the heat and to control the amountof oxygen in the area of the SCR catalyst.

A microemulsion was formed using No. 2 diesel fuel, ethanol (15% byvol.) and a proprietary additive (10%) available from G.E. Betz, TrevosePa. prepared according to WO 02/059236. The mixture was splash blendedto form the emulsion, and transferred to a still. A vacuum of 200 mm Hgwas applied and the still heated to 80° C. (liquid temperature). Thedistillate was collected as a single phase and the percentage of ethanoldetermined by infrared spectrometer to be greater than 98% pure whenapproximately 3% of the total volume was stripped when continued, 90% ofthe available ethanol can be obtained at 95% purity.

The invention has been described with reference to preferred andalternative embodiments of the invention. Modifications and alternativesto the invention will occur to those skilled in the art and it isintended that all such modifications and alterations fall within thescope of the invention and claims.

1. A method to reduce NO_(x), emissions from the exhaust of dieselengines by use of E-diesel fuel and a selective catalytic reducingconverter comprising the steps: distilling out a portion of the ethanolin the E-diesel under reduced pressure, injecting the distilled ethanolinto exhaust gasses from the engine upstream of said selective catalyticreducing converter, controlling said ethanol injection using at leastone engine parameter selected from the group consisting of intake airflow, fuel mixture richness, engine operating temperature and NO_(x)sensor output.
 2. A method according to claim 1 wherein the distillationprocess is performed periodically.
 3. A method according to claim 1wherein the distillation is continuous.
 4. A method according to claim 1wherein the distillation is performed under a vacuum.
 5. A methodaccording to claim 1 wherein the distillation is performed atatmospheric pressure.
 6. A method according to claim 1 wherein theamount of injected ethanol corresponds to the amount of NO_(x) in theexhaust.